1. Field of the Invention
The present invention relates to a honeycomb structure body having a plurality of hexagonal cells formed in a lattice arrangement, and in particular, relates to a honeycomb structure body having a plurality of hexagonal cells in which each hexagonal cell is surrounded by a hexagonal cross-section cell wall composed of six sides. Through the following description, such a honeycomb structure body having a plurality of hexagonal cells will be referred to as “a hexagonal cell honeycomb structure body”.
2. Description of the Related Art
Honeycomb structure bodies have been known as a substrate or a base material for purifying exhaust gas emitted from an internal combustion engine mounted on a vehicle such as diesel engine vehicles and gasoline engine vehicles. The honeycomb structure body has a plurality of cells formed in a lattice arrangement. Each cell is surrounded by cell walls. The honeycomb structure body is mainly made of cordierite of a superior thermal-shock resistance. Catalyst is uniformly supported on the surfaces of the cell walls. That is, the entire surfaces of the cell walls are coated with catalyst. Japanese patent laid open publication No. JP 2002-177794 has disclosed a honeycomb structure body having such a configuration.
The ceramic honeycomb structure body is composed of plural cells and the shape of each cell is triangle, square, or hexagon, for example. A hexagonal cell honeycomb structure body, namely, a honeycomb structure body composed of a plurality of hexagonal cells is capable of easily and uniformly supporting catalyst on the surfaces of the cell walls and capable of reducing pressure loss when compared with a honeycomb structure body of another type composed of triangle cells or square cells. In addition, because each hexagonal cell formed in the hexagonal cell honeycomb structure body is capable of suppressing the formation of excess amount of catalyst on the surfaces of the cell walls, the entire weight of the hexagonal cell honeycomb structure body can be reduced. Considering from the capability of purifying exhaust gas, the hexagonal cell honeycomb structure body has become of major interest, recently. This has been disclosed in Japanese patent laid open publication No. JP 2000-237602.
As described above, although the hexagonal cell honeycomb structure body has a superior function of efficiently purifying exhaust gas emitted from an internal combustion engine of a vehicle, the entire strength thereof is relatively low. In particular, when the hexagonal cell honeycomb structure body does not entirely have a sufficient strength under the use as an exhaust gas purifying substrate, there is a possibility of causing cracks and breaking in the hexagonal cells by vibration and stress generated during a caning step of forcedly caning the hexagonal cell honeycomb structure body into an exhaust gas pipe, and during an assembling step of assembling it into a vehicle.
There is a conventional manner of solving such a drawback, which forms thicker cell walls for the hexagonal cells in order to increase and improve the entire strength of the hexagonal cell honeycomb structure body. This manner however increases the entire weight of the hexagonal cell honeycomb structure body and cannot achieve the recent commercial demand of making a vehicle light and small. In addition, a heavy hexagonal cell honeycomb structure body decrease the function of rapidly warming catalyst supported on the surfaces of cell walls in the hexagonal cells prevents rapid warming. This involves a possibility of reducing the purifying capability of purifying exhaust gas.
Accordingly, the hexagonal cell honeycomb structure body is being asked to increasing the entire strength thereof while maintaining the adequate strength in practical use.